The current invention concerns a process for the manufacture of an optical ribbon conductor from several optical conductors where the outer circumference of at least one optical conductor is coated with a first coating material, where the optical conductor and at least one other optical conductor are arranged beside each other in the longitudinal direction and formed into a ribbon conductor, so that a gap is created between the two adjacent optical conductors which is not occupied by an optical conductor, and where the optical conductors are coated with a second coating material so that the ribbon conductor is surrounded by the second coating material and the gap between the two optical conductors is filled by the second coating material.
During the manufacture of optical conductors it is customary to characterize them with a color-coded coating in order to determine their type and/or use at a later time. For this purpose, the outer circumference of the optical conductor to be characterized is coated with a colored coating material. In order to form several optical conductors into a ribbon conductor during a further processing step, they are arranged beside each other in a longitudinal direction and are coated with second coating material which surrounds the ribbon conductor to be formed.
In order to combine two optical ribbon conductors containing optical conductors after their manufacture, it is necessary to remove the second coating surrounding the ribbon conductor at the ends without removing the colored coating layer beneath it. In this way the optical conductors remain distinguishable. The removal of the second coating surrounding the ribbon conductor in one piece is usually relatively difficult since the two coatings tend to adhere to each other.
The second coating can be removed chemically by means of a solvent. Such a process is generally not environmentally friendly and could be dangerous to the operators. Another method consists in removing the second coating at the ends by thermal means. The coating can be warmed in small sections and then pulled off. The disadvantages of this solution consist in the fact that only relatively small pieces can be removed and the removal must be done with a special tool. Additionally, the colored coating of the optical conductor is removed at the same time which leads to the loss of the characterization of the optical conductor. It is also possible to remove the second coating mechanically. This is generally rather complicated and there is the danger that the colored coating underneath will also be removed.
From EP 0 614 099 A2 it is known to select a coating material for the colored coating and the second coating surrounding the ribbon conductor which contains a part of a dissolving additive, for example, a part of silicone. This reduces the adhesion between the two coatings. Mechanical characteristics are, however, generally worse due to this additive.
A process for the manufacture of an optical ribbon conductor is known from DE 197 02 106 A1. For the manufacture of the ribbon conductor several optical conductors are guided beside each other through the entry of a coating device. The diameters of the optical conductors and/or the position of the optical conductors within the ribbon conductor are determined. The width of the entry opening of the coating device can be changed based on the measured diameter values and/or the size of the gap between two optical conductors. Due to the drag flow of the coating material the spaces between or at the optical conductors are completely filled with the coating material. With optimum centering the optical conductors are directly adjacent to each other.
The optical conductors generally have a predetermined nominal outer diameter. In practice, however, there are deviations in diameter for each optical conductor so that the optical conductors generally show over or under tolerance. Due to diameter values that are too small, a gap can form between to adjacent optical conductors, which is not occupied by an optical conductor. This can be caused by the fact the drag flow forces are no longer strong enough to ensure a completely centered arrangement of the optical conductors.
If the gap shows a certain width, the second coating surrounding the ribbon conductor cannot be completely removed since the second coating material in the space between the optical conductors or in the gap, respectively, does not break up.
The objective of the current invention is to provide a process for the manufacture of an optical ribbon conductor with several optical conductors of a type mentioned in the introduction, which makes it possible to remove the second coating after manufacture in a manner that leaves the coating material underneath.
This objective is achieved by a process for the manufacture of an optical ribbon conductor with several optical conductors of the type mentioned in the introduction, where the position of an optical conductor within the ribbon conductor is controlled by the coating thickness of the second coating material.
By controlling the position of an optical conductor within the ribbon conductor relative to the coating thickness of the second coating material, the width of the gap not occupied by an optical conductor between two adjacent optical conductors is influenced relative to the coating thickness. A gap width results which is relative to the coating thickness. Thus the influence of the coating thickness of the second coating material can be considered for the later removal of the second coating material. The gap width can be measured in such a way, that the second coating material in the space or gap, respectively, between two adjacent optical conductors will be broken during subsequent removal of the second coating material. This makes it possible to remove the second coating material without removing the underlying first coating, for example, a color coating for characterization of an optical conductor.
In further development of the process according to the invention, the position of at least one optical conductor within the ribbon conductor is controlled by the tensile modulus and shear modulus of the second coating material. This has the advantage of considering the individual characteristics of the second coating material during the manufacture of the ribbon conductor, so that the second coating material can be successfully removed after manufacture.
For a preferred version of the process according to the invention, the first coating material is cured, before the second coating material is applied. This is generally done by lamps, which emit UV rays. The UV output of the lamps should be sufficient to cure the first coating material, which, for example, forms the colored coating of the optical conductor. The curing should be done in a nitrogen atmosphere, which has a relatively small oxygen content. The desired oxygen content is 1 to 20 particles per million (ppm). In case the first coating material is not sufficiently cured, the second coating material generally adheres relatively tightly to the first coating material so that the removal of the second coating material becomes more difficult.
In order to keep the gap not occupied by optical conductors as small as possible, or, respectively, to maintain a nominal gap width, it is preferred to optimize the process for applying the first coating material, for example, a coloring process. In this way, diameter deviations of the optical conductors can be reduced during the coloring process. This can be achieved by coating the optical conductors with the first coating material in such a way that a coating thickness between 6 and 9 micrometers (xcexcm) results. This can be achieved by the proper selection of the coloring die of the coating tool.
In further development of the process according to this invention, the first coating material and/or the second coating material is selected in such a way, that the tensile strength of the second coating material is greater than the adhesion strength between the first and second coating material. A relatively elastic second coating material with a relatively high tensile strength enables the simple removal of the second coating material without the first coating material remaining on the second coating material.